Recently, use of the light-wave rangefinder has been studied even in measuring fields other than the surveying field in view of easiness of operation and high precision thereof. However, where the light-wave rangefinder is utilized in the aforementioned measuring fields other than the surveying field, there poses problems in that it is impossible to secure a place where a light-wave rangefinder is installed depending on measuring objects or measuring environment, and that the light-wave rangefinder is adversely affected such that the electronic circuit housed in the light-wave rangefinder undergoes noises.
On the other hand, where an attempt is made to measure the liquid level in a petroleum tank or the like by a lightwave rangefinder, if short-circuiting or spark should occur in the electronic circuit housed in the light-wave rangefinder, there involves a danger in that the flammable gases within the tank would be exploded. Therefore, there poses a problem in that the measuring environment is adversely affected by the light-wave rangefinder such that it is not possible to install a light-wave rangefinder within the tank for measurement.
Moreover, turning now to the surveying field, recently, a so-called "light-wave alidade" in which an alidade and a short-range type light-wave rangefinder are combined has been utilized for a plane-table survey to contribute to labor saving. In this case, however, the large body of the lightwave rangefinder is added to the alidade, and therefore, a problem still remains in manipulation as compared with usual alidades.
The present invention has been made in an attempt to solve all the problems noted above.
It is a first object of the present invention to provide a light-wave rangefinder which can be more widely used than the conventional ones for various measuring fields and objects in various measuring environments.
It is a second object of the present invention to provide a novel light-wave alidade which is smaller in size and easier to manipulate than a conventional light-wave alidade.
It is a third object of the invention to provide a liquid level measuring apparatus in which is utilized a lightwave rangefinder.
It is a fourth object of the invention to provide a liquid level measuring apparatus utilizing a light-wave rangefinder having a photoconduction or light-wave transmission pipe member which can eliminate the measuring error being caused by the vibration or the deformation of the pipe member or liquid containing tank.